The present invention relates to power generation and more particularly to systems and methods for converting wind energy acting on aerial wind driven elements to mechanical or electrical power.
As fossil fuels become depleted and more expensive, the need for cost competitive methods and apparatus for harnessing renewable energy sources increases. The wind was long used for powering sailing ships and windmills, but the advent of steam engines or turbines, internal combustion engines, and gas turbines provided cheaper, more convenient energy sources. Less expensive and more efficient apparatus and methods for utilizing wind power would now be beneficial.
Ground based windmills (or wind turbines) are currently being used to generate electricity and to drive pumps. However, the cost to generate electricity with a wind turbine is still more expensive than the cost of electricity generated from some fossil fuels. Wind turbines have a high capital cost relative to power generated. Wind speed, in general, is higher and more consistent with increasing altitude.
Therefore, to take advantage of the greater force of winds available at higher altitudes it is desirable to make use of airborne or aerial apparatus at altitudes above the heights reasonably reachable by ground-based wind turbines.
Various systems for generating electric or rotary power using wind present at higher altitudes are disclosed in U.S. Pat. No. 7,188,808 titled Aerial Wind Power Generation System and Method which issued March 2007 and U.S. Pat. No. 7,275,719 titled Wind Drive Apparatus For An Aerial Wind Power Generation System which issued to me, Gaylord Olson, Oct. 2, 2007, and whose teachings are incorporated herein by reference, as if fully repeated herein.
By way of example, there is disclosed in U.S. Pat. No. 7,275,719 an aerial power generation system which includes a guide line that extends skywards at a selected angle. The guide line is connected at the upper end to a support body. A wind driven apparatus with a driven element is slidably mounted on the guide line. The driven element uses a sail-like design with curvature about a horizontal axis so as to maximize the lift and drag wind forces, or the driven element includes a rotatable hub with a plurality of airfoil blades. The driven element is connected by a tow line to a reel on a shaft of a power generating means. Means are provided for changing the driven element from high force configurations to low force configurations. The camber of the airfoil driven element is controlled to maximize the force when the driven element is in a high force configuration and to minimize the force when the driven element is in a low force configuration.
Referring to prior art FIGS. 10, 11, and 12 (which correspond to FIGS. 40, 41 and 42 of U.S. Pat. No. 7,275,719) there is shown a flat platform 341 which can rotate about a vertical axis 345 to maintain orientation with respect to the wind direction. Located above the platform is a series of triangular kites 343. These are similar to delta kites, except that instead of a single tether line there is a tether line attached to each one of the three corners of each kite. Triangular kites are used by way of example and the kites could be of any other shape (e.g., rectangular, trapezoidal) with a tether line connected to each corner.
FIGS. 10, 11 and 12 show three small kites 365, which may be radio controlled, to improve the stability of the system and to keep tension in the tether lines regardless of the angle of attack of the triangular kites. These small kites 365 may not be essential to the operation and may be a negative factor in some situations.
FIGS. 10, 11 and 12 show rectangular boxes 342 on top of each corner of the platform 341. At a minimum, there is included in each box a reel for the tether line, a gearbox and a computer controlled motor/generator. This enables power generation.
Still another aspect of the invention is the recognition of the desirability to simplify the system by sharing certain components. For example, in the prior art system there is a motor/generator per tether line. A simpler approach includes having several tether lines transfer power to a single motor/generator.
These aspects of the invention are addressed in systems embodying the invention.